Regenerator



Dec. 27, 1949 w. DENNIS 2,492,788

REGENERATOR 2 Sheets-Sheet 1 Filed May 24, 1947 INVENTOR WOLCOTT DENNlSBY M ATTORNEYS J W- DENNIS REGENERATOR Dec. 27, 1949 2 Sheets-Sheet 2Filed May 24, 1947 INVENTOR WOLCOTT DENNiS RNEYS a ATT Patented Dec. 27,1949 BEGENEBATOR Wolcott Dennis, Darlen, Conn., assignor to AirReduction Company, Incorporated, New York, N. Y., a corporation of NewYork Application May 24, 1947, Serial No. 750,234

1 v This invention relates to improvements in apparatus for cooling afluid by transfer of heat to a heat absorbing mass. the temperature ofwhich has been reduced in warming another fluid from a low temperatureas exemplified in the patent to Frankl No. 1,890,646 in which such asystem is employed in the separation of a gaseous mixture into itsconstituents by liquefaction.

The devices employed for the-purpose described are ordinarily referredto as regenerators or accumulators. In liquefaction processes employingsuch regenerators. air ordinarily passes in through the nitrogenregenerator at about five atmospheres pressure, and nitrogen isexhausted through the regenerator at about 1 atmosphere pressure so thatthe volume ratio of nitrogen to air passing through any temperaturelevel in a regenerator is about 5-1. complete revaporization and removalof carbon dioxide deposited from the air, the vapor pressure of thecarbon dioxide at the nitrogen temperature cannot be less than one-fifththat corresponding to the temperature of the air at the point ofdeposit, since 5 volumes of nitrogen would then contain just as muchcarbon dioxide as was brought in by 1 volume of air. With equal massflows of air and nitrogen, this equalization of carbon dioxide carryingcapacity occurs at a temperature level where about of the carbon dioxidestill remains in the air, and at colder temperatures carbondioxidedeposits are incompletely revaporized due to insufliciently highvapor pressures at the nitrogen temperature. As a result, theregenerator eventually becomes choked with solid carbon dioxide and mustbe warmed to eliminate this material.

One method of altering the conditions in ithe zone where carbon dioxideis not completely revaporized consists of the addition of a smallincrement of flow to the outgoing nitrogen so that it has a greater heatcapacity in relation to the entering air. This results in lower airtemperature at the level corresponding to any given nitrogen temperaturein the colder zones of the regenerator or a higher nitrogen temperatureat the level of any corresponding cold region air temperature. Obviouslythe zone of complete carbon dioxide removal has thus been extended'to alower temperature level, and carbon dioxide revaporization is morenearly complete.

This proposed method has several disadvantages in that the incrementalflow of nitrogen must be suppliedby introducing an'auxiliary air supplywithout passing it through the regenera- In order to achieve 5 Claims.(Cl. 2576) tor. It must be dry and free from carbon dioxide andtherefore require some means for elimination of these impurities. Also,the closer approach of air and nitrogen temperatures at the cold end ofthe regenerator attained by this method results in further separation ofthe air and nitrogen temperatures at the warm end and the consequentloss of refrigeration in the method.

Another proposed method of overcoming the difliculty experienced withregenerators involves removing a portion of the air stream at about themid-point of the regenerator. The reduced quantity of the remaining aircontains less total carbon dioxide and the temperature approach of theremaining air is closer to that of the nitrogen so that any carbondioxide frozen out is easily revaporized by the larger nitrogen stream.This again requires a purification system for that part of the air whichis withdrawn at the mid-point of the regenerator, since otherwise thecarbon dioxide and moisture present therein will be carried over intothe liquefaction system. Even though the total amount of carbon dioxideis small, it may nevertheless introduce difficulties in the system.

It is the object of the present invention to provide an improvedapparatus for effecting the desired heat transfer while ensuring morecomplete revaporization of solids deposited from the incoming fluid suchas air during that part of the cycle when the outgoing fluid such asnitrogen passes through the regenerator.

Other objects and advantages of the invention will be better understoodby reference to the following speciflcation and the accompanyingdrawing, in which Fig. 1 is a longitudinal section through a regeneratorembodying the invention;

Fig. 2 is a section on the line 2-2 of Fig. 1;

Fig. 3 is a section on the line 3-3 of Fig. 1;

Fig. 4 is a longitudinal section through a modifled form'of theregenerator;

Fig. 5 is a section on the line 5-5 of Fig. 4; and

Fig. 6 is a view in perspective of a heat transfer element.

Referring to the drawing, 5 indicates a tubular shell of any suitablemetal having outlets 6 and I at the top and bottom thereof. Air, forexample, is adapted to be introduced through a pipe 8 at the top of theregenerator, and nitrogen, for example, may be exhausted through thepipe 9. A valve In is adapted to be reversed from time to time so thatair and nitrogen pass alternately through the regenerator. At the bottomof the regenerator, pipes II and I2 afford an inlet for nitrogen and anoutlet for air. Valves l3 and copper, aluminum, or the like.

ll may be manipulated in proper sequence with the adjustment of thevalve ill to direct the flow of the fluids alternately through the reenerator.

The shell of the regenerator is substantially filled with a plurality ofcoils II; of corrugated metal ii of copper, aluminum or the like woundabout cores i1. While I prefer to employ filling elements similar tothose described in Frankl Reissue Patent No. 19,140, any suitablefilling material which is adapted to effect heat transfer between thefluids passing through the regenerator may be employed. Preferably thecoils l5 are separated by spacers it, although this is not essential tothe invention because even if the coils are in direct contact the heatflow between them is relatively limited, owing to the insulating effectof the film of gas between the metal surfaces which may be in contact.

In accordance with the present invention, I provide in the lower sectionof the regenerator a plurality of elongated members IQ of metal having ahigh heat conductivity coefiicient such as The members may be in theform of rods, bars, sheets or similar elements having sumcient mass andsurface to effect heat transfer between the several coils IS in thelower section of the regenerator. Heat will thus flow from the warmerregion to the colder end of the regenerator, tending thus to raise thetemperature of the coils l5 at the lowermost or colder end and lower thetemperature of the rods at their upper ends.

Assuming that the regenerator has already been cooled by passage ofnitrogen upwardly therethrough to an adequately low temperature, theflow of nitrogen is shut off and air is introduced from the pipe 8.Flowing downwardly through the regenerator, the air is cooled by heattransfer to the metal of the coils IS. The air will be cooled to a lowertemperature in the upper portion of the zone containing the rods I9 thanit could reach if the packing were not conductive and moisture andcarbon dioxide therein will be congealed and deposited on the metalsurfaces. At the proper time, the flow of air is shut off, and nitrogenis again conducted through the regenerator. The nitrogen, in passingupwardly, is warmed to a warmer temperature in the lower portion of theregenerator including the rods l9, than it could reach if the packingwere not conducting heat to it from a higher zone.

At approximately the mid-point of the heat conducting zone of theregenerator, both effects have reached a maximum, and the temperature oftheair depositing carbon dioxide is much closer to the temperature ofthe nitrogen vaporizing the carbon dioxide than would be possible withthe usual type of regenerator having no substantial heat transferbetween the coils l5. At all points within the zone in which conductivepacking is installed, the temperature difference between the airdepositing carbon dioxide and the nitrogen revaporizing the carbondioxide is less than would be the case if no provision were made forlengthwise heat conduction This closer approach. of the air and nitrogentemperatures results in a relative increase in the carbon dioxide thenitrogen is able to revaporize and carry out of the regenerator agreater proportion of the carbon dioxide, carried to any point of thiszone by the air, than would be the case if no lengthwise heat conductionwere provided.

By the installation of a suflicient number of conductive elements in thecold zone of a regenerator, extending from a temperature level of about-200 F. to the cold end, the temperature approach of the air andnitrogen in this zone can be brought sufllciently close so that completerevaporization and removal of deposited carbon dioxide may be effectedexcept in the very coldest parts of the regenerator. In these parts solittle carbon dioxide remains in the air (less than 0.2% of normalcarbon dioxide content) that no operating difficulty results.

The design of conductive packing for any particular case will depend onthe degree of temperature approach required. the type of packing chosenfor the warm end and the quantity of flow per unit area of theregenerator. To be effective, there must be suflicient heat transfersurface and mass to carry out the normal function of regenerativepacking and compensate for the lower mean temperature differenceresulting when lengthwise heat conductive elements are used. The packingmaterial and its total crosssection area must be selected to conduct theheat necessary to produce the required temperature differentials,..-rticularly in the upper part of the conductive zone where thegreatest concentration of carbon dioxide exists.

In Figs. 4 to 6, a modified form of the regenerator is shown in which atubular shell 20 of any suitable metal is provided with outlets 2| and22 at the top and bottom thereof. Air, for example, is adapted to beintroduced through a pipe 23 at the top of the regenerator, andnitrogen, for example, may be exhausted through the pipe 24. A valve 25may be reversed from time to time so that air and nitrogen passalternately through the regenerator. At the bottom of the regeneratorpipes 26 and 21 afford an inlet for nitrogen and an outlet for air.Valves 28 and 29 may be manipulated in proper sequence with adjustmentof the valve 25 to direct the flow of the fluids alternately through theregenerator.

The shell 20 of the regenerator is partially filled with a heat transfermaterial 30 such for exampleas a multiplicity of small pieces Of metalsupported in a screen 3|. A screen 32 may be disposed above the heattransfer material. Aluminum or copper are preferred, but other materialsmay be used. Conveniently, the material may be in the form of balls orpellets of regular or irregular shape, which afford a multiplicity ofgas passages between them. The size may be approximately one-eighth toone-quarter inch in diameter, but larger or smaller pieces may be used.The heat transfer material 30 i alternately cooled and-warmed by thepassage of the fluid therethrough.

At the lower or cold end of the regenerator, a plurality of elongatedmembers 33 of metal having a high heatconductivity coefficient such ascopper, aluminum or the like are disposed in the space beneath thefilling of heat transfer material. The members 33 may be supported by ascreen 34. The members 33 may be in the form of'rods, bars, sheets orsimilar elements having sufllcient mass and surface to effect heattransfer from the warmertothe colder ends thereof. Heat will'thus, flowfrom the warmer region to the 5 grooves 35 in the surfaces of the rods.The grooves 35 facilitate the passage of fluid around and between therods. The invention is not, however, limited to the use of rods in thisparticular form, since it depends, as hereinbefore indicated,

upon the provision of means to transfer heat from an intermediate to acolder region of the regenerator.

The operation of the modification last described is substantially as inthe preceding embodiment of the invention. Therefore it is unnecessaryto repeat the description of such operation. The resulting advantage isthe same.

The apparatus as described affords an eflective solution of the problemof revaporizing the deposited carbon dioxide from the metal surfaces ofthe regenerator by the available flow of nitrogen. It is thusunnecessary to resort to expedients such as the auxiliary air stream orwithdrawal of a portion of the air from the regenerator before itreaches the colder end thereof.

While the invention has been described more particularly with referenceto the nitrogen regenerators, it may be utilized similarly where oxygenis employed as the cooling fluid, in which case the entering air iscooled by contact with the cold metal surfaces in the regenerator uponwhich it deposits moisture and carbon dioxide in solid form. The latterare re-vaporized, in this case by the flow or cold oxygen in the reversedirection through the regenerator.

Various changes may be made in the form, arrangement and structure orthe apparatus without departing from the invention Or sacrificing theadvantages thereof.

I claim:

1. A regenerator adapted to transfer heat between streams of fluidspassing alternately through the regenerator comprising a. shell having awarm end and a cold end, inlet and outlet means connected to each end01' the shell, heat transfer material aflording a multiplicity of gaspassages of relatively small cross-sectional area within the warm end ofthe shell, and a plurality of heat-conducting members in the cold endpor- 6 tion of the shell and extending longitudinally of the shell fromthe cold end to an intermediate section thereof, said heat-conductingmembers providing continuous heat-conducting paths between saidintermediate section and the cold end of the shell.

2. A regenerator as set forth in claim 1 in which thelongitudinally-extending heat-conducting members have helical grooves ontheir peripheries to facilitate the passage of fluids.

3. A regenerator as set forth in claim 1 in which the heat transfermaterial in the warm end portion of the shell comprises small pieces ofmetal and the longitudinally-extending heat-conducting members are metalrods.

4. A regenerator as set forth in claim 1 in which the heat transfermaterial in the warm end portion of the shell is arranged in consecutivelayers.

5. A regenerator as set forth in claim 1 in which the heat transfermaterial in the warm end portion of the shell is arranged in consecutivelayers, and in which the longitudinally-extending members are of metalhaving a high heat conductivity coeflicient.

WOLCOTT DENNIS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

